The present invention relates to a novel fluorine-containing polymeric compound which is useful as a material of Langmuir-Blodgett's films as well as to a method for the preparation of such a fluorine-containing polymeric compound.
It is known that polymeric compounds modified with long-chain perfluoroalkyl groups have excellent properties such as water- and oil-repellency, insusceptibility to dust deposition, corrosion resistance and the like so that they are used, for example, for protection and surface modification of electronic circuit boards. Further, they are promising as a material of oxygen-permeabIe membranes having improved selectivity for the permeation of oxygen relative to other gases by virtue of the high affinity of the perfluoroalkyl groups to oxygen.
A problem in the use of such a polymeric compound having perfluoroalkyl groups introduced into the molecular structure is that the polymer is hardly soluble in solvents due to the water- and oil-repellency inherent in the perfluoroalkyl groups so that fluorine-containing polymers are generally not handleable as a material of thin films. In other words, fluorine-containing polymeric compounds can be shaped only with great difficulties into an extremely thin film as an essential element when the polymer is used as a material for surface modification or protection of boards. While it is important that the perfluoroalkyl groups as the functional groups for the oil- and water-repellency and other useful surface properties are oriented toward the surface of the polymeric material in order that the desired performance of surface modification and oxygen permeation can be fully exhibited, a general understanding is that control of such an orientation of polymeric molecules is far from possibility.
Preparation of a thin film or so-called Langmuir-Blodgett's film, referred to as an LB film hereinafter, of a fluorine containing polymeric material is reported, for example, by R. Elbert, et al. in Journal of the American Chemical Society volume 106, page 7678 (1984), according to which a fluorine-containing ethylenically unsaturated monomeric compound is spread on the surface of water to form a monolayer film followed by the photopolymerization of the monomer by the irradiation with ultraviolet light. This method is, however, defective in respect of the uncontrollability of the density of the fluorine-containing molecular chain in the monomolecular film and indefiniteness of the degree of polymerization after the photopolymerization.
One of the inventors has been successful in preparing an LB film of a controlled molecular orientation from a polyallylamine modified with perfluoroalkyl groups. These perfluoroalkyl-modified polyallylamines however, are still not quite satisfactory because the polymer cannot be shaped into a thin film when the content of the perfluoroalkyl groups introduced into the polymeric structure is high.